To Ponder (recall…)

Computer Science and Engineering n The Ohio State University

To Ponder (recall…)

o GET, HEADn Request: should be safe (no side effects)n Request has header only (no body)

o PUTn Update (or create): should be idempotent

o DELETEn Delete: should be idempotent

o POSTn Create (or update): changes server staten Beware re-sending!

o HTTP does not enforce these semantics

Computer Science and Engineering n College of Engineering n The Ohio State University

Rails:Routes

Lecture 21


Recall: Rails Architecture


Configuration

o Need to map an HTTP request (verb, URL, parameters) to an application action (a method in a Ruby class)n Framework invokes the method, passing in

parameters from HTTP request as argumentsn Results in an HTTP response, typically with an

HTML payload, sent back to client's browsero These mappings are called routeso Defined in config/routes.rb

n Ruby code, but highly stylized (another DSL)n Checked top to bottom for first match


Basic Routeo Pattern string + application action

n In config/routes.rbn Pattern string usually contains segments

o Example routeget 'status/go/:system/memory/:seg',

to: 'reporter#show'o Matches any HTTP request like

GET /status/go/lander/memory/0?page=3o Result:

n Instantiates ReporterControllern Invokes show method on that new instancen Provides an object called params (like a hash)params = { system: 'lander',

seg: '0',page: '3' }


Default Valueso Special segments

n :controller - the controller class to usen :action - the method to invoke in that controller

o Example routeget ':controller/go/:action/:system'

o Matches any HTTP request likeGET /reporter/go/show/lander?page=3

o Result:n Instantiates ReporterControllern Invokes show method on that new instancen Provides an object called paramsparams = { system: 'lander',

page: '3',# also :controller and :action }


Customizing Routes

o Recognize different HTTP verb(s)n get, put, post, deleten Alternative: match via: [:get, :post]

o Optional segments with ( )get ':controller(/:action(/:id))'

o Default values for paramsget 'photos/:id', to: 'photos#show',

defaults: { format: 'jpg' }


REST

o REpresentational State Transfern An architectural style for web applicationsn Maps database operations to HTTP requests

o Small set of database operations (CRUD)n Create, Read, Update, Delete

o Small set of HTTP verbs, with fixed semantics (e.g., idempotence)n GET, POST, PUT, DELETE

o The protocol is statelesso Resource: bundle of (server-side) state

n Each resource is identified by a URL


Resources

o A resource could be an individual membern Example: a single studentn Corresponds to a row in a table

o A resource could be a collection of itemsn Example: a set of studentsn Corresponds to a table

o In REST, resources have URLsn Each member element has its own URL

http://quickrosters.com/students/42

n Each collection has its own URLhttp://quickrosters.com/students


Read Collection: GET

Request

GET /students HTTP/1.1Host: quickrosters.com



Request

GET /students HTTP/1.1Host: quickrosters.com




HTML Source (GET Collection)…<h1>Students</h1><table><tr><th>Fname</th><th>Lname</th><th>Buckid</th><th colspan="3"></th>

</tr>…<tr><td>Primo</td><td>Carnera</td><td>334432</td><td><a href="/students/3">Show</a></td><td><a href="/students/3/edit">Edit</a></td><td><a href="/students/3" data-confirm="Are you sure?"

data-method="delete" rel="nofollow">Destroy</a></td></tr>

…</table><a href="/students/new">New Student</a>


Read Member: GET

Request

GET /students/3


Minimal Set of Routes (R)

Collection/students

Member/students/42

GET List all members Show info about a member

PUT

POST

DELETE


Minimal Set of Routes (CR)

Collection/students

Member/students/42


PUT

POST

DELETE

o How to map “create member” action?n Member doesn’t exist è target is collectionn Creation is not idempotent è verb is…


Minimal Set of Routes (CR)

Collection/students

Member/students/42


PUT

POST Create a new member

DELETE

o How to map “create member” action?n Member doesn’t exist è target is collectionn Creation is not idempotent è verb is…


Minimal Set of Routes (CRU)

Collection/students

Member/students/42


PUT


DELETE

o How to map “update member” action?n Target is a membern Update overwrites, so it is idempotent…


Minimal Set of Routes (CRU)

Collection/students

Member/students/42


PUT Update member


DELETE

o How to map “update member” action?n Target is a membern Update overwrites, so it is idempotent…


Minimal Set of Routes (CRUD)

Collection/students

Member/students/42


PUT Update member


DELETE Delete this member

o Delete action destroys a member


Minimal Set of Routes

Collection/students

Member/students/42


PUT Update member



o Implicationsn You can't delete a collectionn No idempotent operations on collection


Typical Workflow: Delete

o How does one destroy a member?n Need to issue an HTTP request:DELETE /students/4

o Protocol:n GET the collection to see the listn Click a button next to one item in the list

to issue a DELETE for that membero Alternative:

n GET the member to see the detailsn Click a button to issue a DELETE for that

member


GET List, DELETE Member

GET /students

DELETE /students/4


Typical Workflow: Create

o How does one issue a POST on collection?n GET a (blank) formn Fill in fields of formn Click a button to submit, resulting in the

POSTo That first GET is a new route

n GET on the collectionn But instead of a list of members, the

result is a form to be filled in and submitted


GET Blank Form, POST the Form

GET "a blank form"

POST /studentslname: …etc


Standard Set of Routes

Collection/students

Member/students/42

GET 1. List all members2. Form for entering a new member's data

1. Show info about a member

PUT Update member




HTML Source…<h1>Students</h1><table><tr><th>Fname</th><th>Lname</th><th>Buckid</th><th colspan="3"></th>





Typical Workflow: Update

o How does one issue a PUT on a member?n GET a (populated) formn Edit the fields of the formn Click a button to send, resulting in the

PUTo That first GET is a new route

n GET on a membern But instead of a display of information

about that member, the result is a populated form to modify and submit


GET Filled Form, PUT the Form

GET "a populated form"

PUT /students/4lname: …etc


Standard Set of Routes

Collection/students

Member/students/42

GET 1. List all members2. Form for entering a new member's data

1. Show info about a member2. Form for editing an existing

member's dataPUT Update member




HTML Source…<h1>Students</h1><table><tr><th>Fname</th><th>Lname</th><th>Buckid</th><th colspan="3"></th>





Rails Resource-Based Routeso For a resource like :students, the action pack

includesn 1 controller (StudentsController)n 7 routes (each with a method in controller)n 4 Views (list of students, show 1 student, new, edit)

HTTPVerb

URL Resource Method Response(View)

GET /students Collection index list allPOST /students Collection create show oneGET /students/new Collection new blank formGET /students/3 Member show show oneGET /students/3/edit Member edit filled formPUT /students/3 Member update show oneDELETE /students/3 Member destroy list all


Defining Resource-Based Routes

o In RosterTool app’s config/routes.rbRails.application.routes.draw do

resources :studentsresources :faculty

end


Customizing Routeso To change which 7 routes are created

resources :students, except:[:update, :destroy]

resources :grades, only: [:index, :show]o To specify a particular controller

resources :students, controller: 'ugrads'o To rename certain actions

resources :students, path_names:{ create: 'enroll' }

o To add more routes to standard setn Add GET /students/:id/avatar (i.e. on member)n Add GET /students/search (i.e. on collection)resources :students doget 'avatar', on: :memberget 'search', on: :collection

end


Segment Keyso URL request has arguments for controller

n Example: products/42n Pattern string: 'products/:id'

o Segment key gets value when route matches

o Controller gets a hash (called params) of segment keys and their valuesn Example: params[:id] is '42'

o Common case: Look up an item by iddef set_product@product = Product.find(params[:id])

end


Recognition vs Generationo Dual problems

n Recognize a URL (request for an action)n Generate a URL (a hyperlink or redirect)

o Routes used for both!o For generation, route must be named

get 'status/:seg', to: 'reporter#show',as: :info

o Results in two helpers (_path, _url)info_path(4)#=> "/status/4"info_url(4) #=> "http://faces.com/status/4"

o Used with link_to to generate hyperlinkslink_to 'S', info_path(4), class: 'btn'#=> "<a class='btn' href='/status/4'>S</a>"


Helper Methods for Resourceso Resource-based routes have names

photos_path #=> /photosphotos_url #=> http://faces.com/photosnew_photo_path #=> /photos/newphoto_path(:id) #=> /photos/4edit_photo_path(:id) #=> /photos/4/edit

Name HTTP URL Resource Method

photos GET /photos Collection index

POST /photos Collection create

new_photo GET /photos/new Collection new

photo GET /photos/3 Member show

edit_photo GET /photos/3/edit Member edit

PUT /photos/3 Member update

DELETE /photos/3 Member destroy


Debugging Routes and Helperso To see the full list of routes

$ rails routesPrefix Verb URI Contr#Actioninfo GET /status/:seg reporter#show

photos GET /photos photos#indexPOST /photos photos#create

photo GET /photo/:id photos#showedit_photo GET /photos/:id/edit ……etc…

o To see/use helpers in the console$ rails console> app.edit_photo_path(42)=> "/photos/42/edit"> helper.link_to "Click here",

app.edit_photo_path(42)=> "<a href="/photos/42/edit">Click here</a>


Root Route

o With no matching route, GET for http://example.com gets index.html from application's public directory

o To customize landing page, 2 choices:n Create public/index.htmln Add root route to config/routes.rb,

pointing to a controller#action (better)root to: "welcome#index"


Singleton Resourceso Declared with singular syntax

resource :systemo You get only 1 resource, not 2

n Controller still plural (e.g., SystemsController)n URLs are singular (e.g., /system/edit

o Only 6 standard routesn No index collection action to list membersn POST /system -> createn GET /system/new -> newn GET /system/edit -> editn GET /system -> shown PUT /system -> updaten DELETE /system -> destroy


Summary

o REST and CRUDn Create, read, update, destroyn Map data to resourcesn Map actions to HTTP requests (verb +

URL)o Routes

n Connect HTTP request to specific method in a controller class

n Defined in config/routes.rbn Resource based, or match-basedn Dual problem: recognition and generation

Documents

To Ponder (recall…)